In conventional fluorescent organic light-emitting devices using a host and a fluorescent dopant, only singlet excitons, which are formed at a ratio of 25% of excitons generated under electrical excitation condition, are emitted, thereby failing to obtain a high efficiency. Meanwhile, in phosphorescent organic light-emitting devices using a phosphorescent dopant instead of a fluorescent dopant, all singlet and triplet excitons can be subjected to conversion to generate light, thereby achieving a high efficiency. However, due to high prices of a phosphorescent dopant, it is disadvantageous to use phosphorescent organic light-emitting devices in terms of an economic aspect. In this regard, there are ongoing studies of a delayed fluorescent dopant, which improves a device efficiency by increasing singlet excited states of a fluorescent dopant by converting triplet excited states to singlet excited states by reverse intersystem crossing (RISC). However, such a delayed fluorescent dopant has a wide emission spectrum and a lifetime of devices which include the delayed fluorescent dopant needs to be verified.